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2000 WR400 - sudden loss of all mid / top power & red exhaust

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I've tried to do due diligence searching forums, but to no avail. 

In the summer, suddenly out of nowhere, I felt it lose all mid to top power and it got very hot very fast, like a plugged jet might do. Started and idled just fine, like it always did.  In neutral, it struggled to build RPM and sounds very weak and flat.

Oddly after a 10 minute rest, it was fine. Weeks later, happened once more too, then after a break ok again.

Then in November, it happened and did not go away. It was burning a ton of oil, knew I needed do it, so I decided it was time to do the top end. Also stripped & cleaned carb. Once back together and started, it acted exactly the same.  Easy start & idle, flat trying to rev. Took carb down again, cleaned it again thoroughly, did the mid body too, new jets & needle, put it back. Does exactly the same thing.

My next step is going to be to remove spark arrestor baffle and try it, may be plugged from all the oil I was burning, it was quite smoky all year. Looked like a 2T.

If you're interested, this is a 15 second video with sound of it running after the new top end. Around 10-12 second mark I'm giving it throttle and it won't rev up further. https://1drv.ms/v/s!AkjfYJ2UrH1Mx_txfVdH39XxCUmEFA?e=vKghfe

I'll follow up with the results of running without the arrestor later. Any suggestions? Thank you.

Edit: spark arrestor not plugged, no change.  Used (unlit) mapp gas to see if I could find vacuum leak, nothing found. Allow mapp gas into intake, rpm's came up stronger but not normal. Wish I had a spare carb to try.

Edited by galbro

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what color are the spark plugs coming out? Sounds like your getting no spark past idle. I would go through testing the ignition components  and magneto.

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The plug is black and possibly dampish. VOM tests on the coil, TPS, cdi pickup, and stator power coils all appear within spec according to shop manual. Previous owner left notes on the page with his measured readings too, and my numbers match well enough.

I've got a variable gap spark tester coming monday, so I should be able to directly observe how good of a spark I'm getting. Starting to think maybe my carb is still screwed up even though I did a cleanup & rebuild kit. I'm no carb pro. I can turn a wrench just fine, but I'm not a diagnostician.

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Yeah sometimes those passages really get plugged up, If your plug is black and wet it’s too rich. Your local shop may be able to put your carb in a sonic parts cleaner if you bring it to them. Or buy your own.

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Sadly, I did all that, even bought a sonic cleaner too. Can't guarantee I found and cleaned all the required passages. I'm tempted to try one of the cheap clone carbs that can be found on ebay and amazon.

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Well dropped in a replacement clone carb. Now I find myself fighting a no spark scenario. While waiting for it, I had removed the stator for inspection, put it all back. I've verified the stator coil resistances, ignition coil resistances, kill switch. 

Anyone know what voltages I can expect from stator on kicking? Enough to blink a 12v test light? What about the orange feeding the coil? 

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Alright then. Just installed a replacement CDI and coil, bought a used set with wiring harness and regulator off ebay. After kicking a hole in my shoe the unburned fuel cleared out and it fired up, and sounds to be running strong as ever. With the original carb too, I put the clone to the side and will probably sell it.

I'm guessing the CDI was dying and then finally kicked the bucket. I suspect the weakened spark left a lot of unburned fuel to burn in the exhaust header, causing it to massively overheat and fooling me into thinking it was a lean-out condition from a clogged jet. 

In other words, dumbass solves problem after many dead ends.

Edited by galbro
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9 hours ago, galbro said:

Alright then. Just installed a replacement CDI and coil, bought a used set with wiring harness and regulator off ebay. After kicking a hole in my shoe the unburned fuel cleared out and it fired up, and sounds to be running strong as ever. With the original carb too, I put the clone to the side and will probably sell it.

I'm guessing the CDI was dying and then finally kicked the bucket. I suspect the weakened spark left a lot of unburned fuel to burn in the exhaust header, causing it to massively overheat and fooling me into thinking it was a lean-out condition from a clogged jet. 

In other words, dumbass solves problem after many dead ends.

Thank you for updating almost no one does after they find the problem and then anyone searching for same problem doesn't know what the fix could be.

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